This invention relates generally to electronically controlled fuel injectors and, more particularly, to a method and apparatus for trimming, i.e., determining and recording for future use data associated with the operating characteristics of a fuel injector prior to installation into an engine, the injector being operable to deliver multiple fuel shots during a fuel injection event.
Electronically controlled fuel injectors are well known in the art including hydraulically actuated and mechanically actuated electronically controlled fuel injectors. An electronically controlled fuel injector typically injects fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are increasingly becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, particulate and nitrogen oxides (NOx). Tailoring the number and the parameters of the injection fuel shots during a particular injection event are ways in which to control emissions and meet such emission standards. As a result, techniques for generating split or multiple fuel injections during an injection event have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emissions and noise levels. Generating multiple injections during an injection event typically involves splitting the total fuel delivery to the cylinder during a particular injection event into two or more separate fuel injections, generally referred to as a pilot injection fuel shot, a main injection fuel shot and/or an anchor injection fuel shot. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control.
In the past, the controllability of split or multiple injections has been somewhat restricted by mechanical and other limitations associated with the particular types of injectors utilized. For example, when delivering a split or multiple injection current waveform to a plurality of fuel injectors, some injectors will actually deliver the split fuel delivery to the particular cylinder whereas some injectors will deliver a boot fuel delivery. A boot type of fuel delivery generates a different quantity of fuel as compared to a split type fuel delivery since in a boot type delivery, the fuel injection flow rate never goes to zero between the respective fuel shots. Conversely, in a split fuel delivery, the fuel injection flow rate does go to zero between the respective fuel shots. As a result, more fuel is delivered in a boot type delivery as compared to a split fuel delivery. Even with more advanced electronically controlled injectors, during certain engine operating conditions it is still sometimes difficult to accurately control fuel delivery.
When dealing with split or multiple fuel injection and the general effects of a boot type fuel delivery and the fuel injection rate shaping which results therefrom, desired engine performance is not always achieved at all engine speeds and engine load conditions. Based upon operating conditions, the injection timing, fuel flow rate and injected fuel volume are desirably optimized in order to achieve minimum emissions and optimum fuel consumption. This is not always achieved in a split or multiple injection system due to a variety of reasons including limitations on the different types of achievable injection rate waveforms and the timing of the fuel injection shots occurring during the injection event. As a result, problems such as injecting fuel at a rate or time other than desired within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy. From an emissions standpoint, either a split or boot fuel delivery may be preferable depending on the engine operating conditions.
In a system in which multiple injections and different injection waveforms are achievable, it is desirable to control and deliver any number of separate fuel injections to a particular cylinder so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time. This may include splitting the fuel injection into more than two separate fuel shots during a particular injection event and/or adjusting the timing between the various multiple fuel injection shots in order to achieve the desired injector performance, that is, a split or a boot type fuel delivery, based upon the current operating conditions of the engine.
Due to limitations in the tolerances achievable during the injector manufacturing process, each injector has its own operating nuances. Therefore, to achieve the desired control of the performance characteristics of the fuel injectors in a given fuel injection system such as an internal combustion engine, it is advantageous to know the operating characteristics of each injector before it is installed into the fuel injection system.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, there is disclosed an electronically controlled fuel injection test system which is capable of simulating the operating characteristics of an internal combustion engine for the purposes of testing an injector before it is installed into an engine to determine and record for future use data associated with the operating characteristics of a fuel injector prior to installation into an engine. The tested injector is capable of delivering multiple fuel injections during a single injection event. For example, when three injections are desired, the first injection is known as a pilot shot, the second injection is known as a main shot and a third injection is known as an anchor shot.
An associated current signal pulse delivered by the test system controls initiation of each shot. A delay exists between the start of the current signal pulse and the start of the respective fuel injection or fuel shot initiated by the pulse due to the time necessary for the injector to respond to the control signal pulse. This delay, known as the start-of-current start-of-injection delay (SOC/SOI), may vary in duration for each shot in an injection event.
An anchor signal delay separates the main and anchor pulses. If the anchor signal delay is of sufficient duration, it will yield a cessation in fuel flow for a period of time, thereby separating the main and anchor shots. This period of time is known as the anchor delay. If the anchor signal delay is not of sufficient duration, the fuel flow will not go to zero between the respective shots and a boot condition will occur.
The present system includes means for variably determining the number of fuel injections or fuel shots desired during a fuel injection event at given simulated engine operating conditions including at a pre-selected pilot, main and anchor fuel injection flow rate, a pre-selected pilot and main SOC/SOI delay, and an anchor delay. The present system also includes means for varying the timing and duration associated with the pilot, main and anchor shots, as well as the duration of the anchor delay.
Under certain operating conditions, the proximity of the main and anchor shots and the resultant internal injector hydraulics and/or mechanics leads to a rate shaping effect of the third or anchor injection. As a result, although the first or pilot injection, when used, is typically a distinct injection as compared to the second and third injections, a distinct third injection is not always apparent. The present invention enables determination as to whether a given injector is delivering a distinct third shot and, based upon considerations such as simulated engine performance, simulated minimization of emissions, injector durability and so forth, the present system adjusts the duration of the main current signal pulse and/or the anchor signal delay, if necessary, to achieve the desired injector performance. However, the techniques disclosed may be applied whenever two signals are located closely togther in time or distance.
These and other aspects and advantages of the present invention will become apparent upon reading the detailed description in connection with the drawings and appended claims.